560SL Idle Speed Control Unit Test Part 1

[BabyBlueBenz]

My '86 has been experiencing the Treaded High-Idle Syndrome (I'll call it THIS), which has been discussed at length on this and other forums. Based on what I learned on the forums and a cursory reading of the MB service manual documents related to the subject, I determined that my Throttle Valve Switch (TVS) had gone bad. As indicated by my in-dash tachometer, my idle was previously around 1500 rpm, then dropped to about 1100 after the TVS was replaced. I also replaced the Idle Speed Air Valve (ISAV) on principal, since it is a key component affecting the engine's idle.

Not satisfied, I continue to scrutinize all factors related to THIS...and there are a lot of potential sources of trouble.

First, I must stress to anyone interested in fixing their own MB vehicle that although these enthusiast's forum are a great asset, YOU MUST INVEST IN A SERVICE MANUAL. Believe me it's worth it getting one. The folks on these forums are a helpful lot, but they're not always going to be there to answer your questions and sometimes they answer incorrectly. The R/C107 series was produced for 17 years (the longest of any MB model) and given all its variations, it's difficult for even the experts to know every detail. The manual itself can be confusing, as the accretion of references builds up as you research a subject. To avoid more confusion, I will attempt to use the terminology as presented by MB in its documents.

That being said, here is my (currently incomplete) experience with testing the heart of the 107's idle management system, the Idle Speed Control Unit (ISCU). I am attempting to perform every task within the manual's procedure with just minimal resources that a shadetree mechanic has (although I've been buying new tools recently) .